The preferred embodiments of the present invention generally relate to a satellite communications system, and more specifically to methods and apparatus for controlling and adjusting spot beam configurations formed by communications satellites that are relocatable between multiple orbital positions.
Communications satellite systems have been proposed that utilized satellites located in a geostationary (GEO) orbit at fixed orbital positions about the earth. The geostationary satellites are placed in orbit at fixed orbital positions to cover one or more land masses. The geostationary satellites generally remain at a predetermined orbital position throughout the life of the satellite. Typically, geostationary satellites include antennas, each comprising a reflector and one or more horn feeds that generate a pattern of spot beams designed to cover an entire target land mass. Each spot beam receives and transmits data signals to and from the satellite. Examples of proposed satellite systems include the Direct TV(trademark) Network, Space Way(trademark) proposed by Hughes, and AstroLink(trademark), proposed by the assignee of the present invention.
In GEO satellite systems, the satellites maintain a fixed position with respect to the earth""s surface in order to cover continuously a desired portion of the earth. Thus, as the earth rotates, a geostationary satellite rotates at a speed necessary to maintain a fixed line of sight at all times with a fixed portion of the earth.
Conventional and previously proposed GEO satellite systems have certain drawbacks. Satellites that use reflector antennas include one or more horn feeds in a feed pattern on an antenna platform. A spot beam pattern is determined when designing the satellite communication system, and the spot beam pattern defines the feed pattern, including the number and arrangement of feeds relative to one another, and relative to a reference point on the satellite. Conventionally, the feed pattern is designed for a particular satellite. For example, geostationary satellites intended for use over the United States are configured with a feed pattern designed to produce spot beams that cover a long rectangular land mass extending from California to Maine.
However, once the antenna is manufactured and fitted on the satellite, the satellite is best suited for coverage only over the United States. The same satellite is not configured with an antenna designed for use over a different land mass shape, such as Europe, Australia, Africa and the like. Europe, the United States and other land masses are shaped differently and include major metropolitan areas located in different relations with respect to one another. For instance, the United States includes major metropolitan areas in Los Angeles, Chicago and New York, that are configured relative to one another in a different manner than the major metropolitan areas of Europe, such as London and Paris. Thus, when designing a satellite antenna, different feed patterns are used on a satellite intended to cover the United States versus a satellite intended to cover Europe. Also, different signal attributes (e.g., bandwidth, power, etc.) are assigned to various horn feeds based upon the corresponding spot beams and geographic market areas. Horn feeds supporting Chicago are assigned more bandwidth and/or power than horn feeds supporting Montana. Hence, conventional and previously proposed antenna and satellite designs are limited to use with specific land masses and market areas, and are not interchangeable or moveable. A disadvantage of conventional and previously proposed satellite systems is the lack of interchangeability.
Also, the demographics and/or communications demands of a particular market may change or evolve in an unexpected or unpredicted manner. For instance, demand within the Midwestern United States may change or fail to increase at a projected rate. Therefore, a satellite previously designed and launched to meet a particular need in the Midwestern U.S. may not be utilized fully. Further, demand may increase at an unexpectedly high rate in the Southeastern U.S., thereby overloading the satellite resources available to that area. Conventional designs would require a new satellite to be manufactured and launched in order to operate optimally for lower Midwestern demand and higher Southeastern demand. It is undesirable to launch new satellites to meet these needs.
A need remains for a communications satellite system having satellites, each of which is capable of operation over multiple separate land masses. A need also remains for a communications satellite system capable of dynamically changing its capacity to meet new and unexpected market needs and to facilitate the phased-in introduction of new satellites. It is an object of the preferred embodiments of the present invention to meet these and other needs that will become apparent from the description set forth below of the preferred embodiments.
A method is provided for controlling a configuration of spot beams produced by a communications satellite. The method includes generating a first plurality of spot beams from the communications satellite maintained at a first orbital position with respect to a first portion of the earth. The first plurality of spot beams are configured in a first beam pattern to encompass substantially a first portion of the earth. The satellite is moveable to a second orbital position with respect to a second portion of the earth. A second plurality of spot beams are configured in a second beam pattern to encompass substantially the second portion of the earth. According to at least one preferred embodiment, at least one common spot beam is utilized in the first and second pluralities of spot beams. Alternatively, the spot beams in the first and second pluralities of the spot beams may be mutually exclusive of one another. When a satellite is moved to a second orbital position, at least one new spot beam is typically activated and at least one old spot beam is typically deactivated.
According to an alternative embodiment, a method is provided that includes changing at least one signal attribute of at least one spot beam included in the first and second pluralities of spot beams. The signal attribute may be one of bandwidth, power and the like. When the satellite is moved from the first orbital position to the second orbital position, a spot beam utilized in both configurations may be rerouted through a new signal path in the satellite.
According to an alternative embodiment of the present invention, a communications satellite is provided having at least one antenna for transmitting and receiving communications signals. The antenna defines first and second ground cell coverage patterns associated with first and second portions of the earth when the satellite is located at first and second orbital positions, respectively. The satellite includes a switch network activating a first group of spot beams forming the first ground cell coverage pattern when the satellite is located in the first orbital position. The switch network activates a second group of spot beams forming the second ground cell coverage pattern when the cell is located at the second orbital position.
The antenna may include a plurality of horn feeds, each of which generates one spot beam when activated. One horn feed may be used to generate a spot beam in each of the first and second groups of spot beams directed to different portions of the earth. The antenna may further include multiple horn feeds divided into first and second groups. The switch network activates the first and second groups of horn feeds to generate first and second groups of spot beams, respectively, when the satellite is moved between the first and second orbital positions, respectively. The first horn feed group may include at least one horn feed not in a second horn feed group.
The satellite may further include multiple signal processors, each of which supports a different type or range of signal attributes such as bandwidth and/or power capabilities. The switching network may connect groups of spot beams to each signal processor depending upon the needs of the spot beam. For instance, beams having low demand require narrow bandwidth, and thus may be assigned to a signal path associated with one or more signal processors having a narrow bandwidth capacity. Similarly, beam spots having high demand require wide bandwidth and thus may be assigned to signal paths associated with signal processors capable of supporting a wide bandwidth.
In yet another further alternative embodiment, the communications satellite is provided with an antenna having multiple horn feeds capable of generating multiple spot beams. The horn feeds are divided into subsets that may or may not include common feeds. The feed subsets are activated separately based upon the orbital position of the satellite.
In yet a further alternative embodiment, a satellite communications system is provided, including user terminals for transmitting and receiving communications signals. The terminals are located around the earth in various cells. The system includes at least one satellite orbiting the earth at a predefined orbital position. The satellite includes an antenna having an array of horn feeds generating spot beams associated with the cells on the earth. The satellite activates different groups of horn feeds on the antenna to form different spot beam patterns associated with different predetermined orbital positions. The user terminals may include a gateway for relaying communications signals between a satellite and a land based communications network, such as a phone system, the internet, intranet, a wide area network, a local area network, and the like.
The system may further include a control terminal directing the satellite to move from one orbital position to another, such as when demand justifies the change. A satellite may be moved when another satellite fails in order to replace the failed satellite. Alternatively, a satellite may be moved when market demands change or do not reach expectations. For instance, a satellite having wide bandwidth may be centered over a portion of the United States expected to require large demand. However, after in use, it may be determined that the satellite""s capabilities are not fully being utilized and may be better suited over a different land mass. As yet a further alternative, the satellites may be moved during the initial introduction of a constellation of satellites. All satellites in a system are typically not launched at the same time. Thus, for example, it may be desirable to locate a single satellite over the Atlantic Ocean in order to cover simultaneously the Eastern United States and Western Europe. Once a second satellite is launched, it may be desirable to move the first satellite to a location over the United States, while positioning the second satellite over Europe.
As a further alternative embodiment, the satellite system may switch individual beam spots between various signal paths when a satellite is moved between positions. The satellite switches spot beams in order to connect a particular spot beam spot to a different signal processor affording different signal attributes, such as more or less bandwidth, lower or higher power, and the like.